1. Field of the Invention
This invention is in the field of magnetic recording media including a non-magnetic base and a magnetic layer containing magnetizable particles dispersed in a binder. The invention is concerned with an improved lubricating layer consisting of one or more organo-polysiloxane compounds.
2. Description of the Prior Art
A magnetic recording medium which is used for audio recording, video recording, or other magnetic recording purposes during use is in contact with guide members, magnetic heads, and the like. In the case of a video tape recorder, where high tape velocities are encountered, the tape must have sufficiently high wear resistance and a relatively small friction coefficient if it is to run smoothly and steadily for a long time. Moreover, the magnetic powder layer including magnetizable particles on such a recording medium must be sufficiently bound to the base to resist shedding or loosening of the powder during use. The magnetic tape must also have good splicing ability.
Magnetic recording media which have relatively high friction coefficients vibrate at the guide members and/or the magnetic heads during recording and/or reproducing so that the recorded signals or the reproduced signals deviate from the original signals with respect to frequency. In some cases, fluttering of the magnetic recording medium can occur to produce the so-called "Q" sound due to the vibration of the recording media.
Various attempts have been made to overcome the above-described defects and to impart lubricity or smoothness to a magnetic recording media, but no completely satisfactory lubricant for magnetic recording media has yet been developed. For example, it has been suggested to use solid lubricants such as molybdenum disulfide, graphite or a wax such that the lubricant is mixed into the magnetic layer containing a magnetic powder such as gamma-Fe.sub.2 O.sub.3, and a binder, such as polyvinyl chloride. Such solid lubricants are ineffective to improve the durability of the magnetic recording media. When a large quantity of the solid lubricant is mixed into the magnetic layer, the magnetic performance of the recording media is impaired. It has also been suggested to use lubricants such as higher fatty acids or esters, or paraffinic hydrocarbons and silicone oils such as dimethylsilicone oil or diphenylsilicone oil as lubricating agents. These lubricants do not provide sufficient durability and lubricity so that magnetic recording media containing these lubricants cannot be effectively used in cassettes for video tape recorders. Magnetic recording media containing large quantities of such lubricants may cause "bleeding" or "blooming" resulting from the lubricant oozing or diffusing onto the surface of the magnetic layer and becoming separated therefrom. Bleeding or blooming which occur on the magnetic layer may cause a stick-slip in which layers of tape wound upon themselves stick to each other.
It has further been suggested that certain organopolysilicone compounds could be employed as lubricants for providing lubricity to magnetic recording media. For example, U.S. Pat. No. 3,993,846 to Higuchi et al discloses a polyoxyalkylene substituted silicone compound having the formula: EQU RO(CHR"CH.sub.2 O).sub.n.sbsb.1 (SiCH.sub.3 CH.sub.3 O).sub.m (CH.sub.2 CHR"O).sub.n.sbsb.2 R'
(wherein R and R' stand for an aliphatic hydrocarbon group having from 8 to 18 carbon atoms, R" is a hydrogen atom or methyl group, m is an integer ranging from 1 to 15 and n.sub.1 and n.sub.2 are integers whose sums range from 2 to 16).
This lubricant exhibits considerable promise in providing an improved magnetic recording medium wherein at least some if not all of the aforementioned prior art problems are alleviated.
U.S. Pat. No. 4,007,314 to Higuchi et al discloses an organosilicone lubricant compound having the formula: EQU (RCOO).sub.n Si(CH.sub.3).sub.4-n
(wherein R is an aliphatic hydrocarbon group containing from 7 to 17 carbon atoms and n is an integer ranging from 1 to 3).
This lubricant also exhibits considerable promise in providing a magnetic recording medium with improved lubrication properties.
Hirano et al in U.S. Pat. No. 4,131,717 disclosed a magnetic recording medium including a non-magnetic base and a magnetic layer thereon which contains and/or is coated with an organopolysiloxane having an average unit represented by the formula: EQU (CH.sub.3)(RO).sub.n (R'COO).sub.m SiO.sub.3-n-m/2
(wherein R is a monovalent hydrocarbon group having from 1 to 5 carbon atoms, R' is a monovalent aliphatic hydrocarbon group having from 7 to 17 carbon atoms, n is zero or a positive number, m is a positive number provided that n+m is less than 3 and the number of Si atoms in a molecule of such organopolysiloxane ranges from 2 to 8).
Magnetic recording media containing such lubricants exhibit a substantially reduced dynamic friction coefficient and a substantially reduced tendency for the magnetic layer to lose its magnetic properties, along with an improved splicing ability.
In U.S. Pat. No. 4,007,313 to Higuchi et al there is disclosed a lubricant for magnetic recording media comprising an organosilicone-fluoride compound having the formula: ##STR2## (wherein R is an aliphatic hydrocarbon group having from 7 to 17 carbon atoms and n is an integer ranging from 1 to 3).
This lubricant also exhibits considerable promise in providing an improved magnetic recording medium.
While the lubricants disclosed in the above prior patents are improvements over prior art lubricants, it is nevertheless desirable to provide even further improved lubricants for use with magnetic recording media.